The present invention relates to a semiconductor device including a multi-stage amplifier circuit composed of semiconductor integrated circuits (referred to as ICs hereinafter) and particularly, a function of inspecting high-frequency amplifier circuits capacitively coupled to each other.
In a step of production of ICs, a group of ICs formed on a semiconductor wafer are subjected to probing a process for inspecting the function of each circuit, with probes the touching pads of the circuit in order to find defective circuits. For this purpose, each IC is equipped with pads for connection to external input/output signals and a power source as well as the pads for the probing test.
FIG. 3 is a schematic diagram of a conventional semiconductor device including a multi-stage amplifier circuit composed of ICs.
The conventional semiconductor device has a pad 1 which is provided for receiving an input signal IN and connected to the input of an amplifier circuit 2. The output of the amplifier circuit 2 is connected to the input of another amplifier circuit 4 by a coupling capacitor 3 which blocks direct-current components. The output of the amplifier circuit 4 is connected to a pad 5 for releasing an output signal OUT. The two amplifier circuits 2 and 4 are connected to common pads 6 and 7 for a power supply. The output of the amplifier circuit 2 also extends to a test pad 8, while the input of the amplifier circuit 4 is joined to a test pad 9.
For the probing test, probes extending from a test system, not shown, are applied directly to the pads 1 and 5-9. The pads 6 and 7 are loaded by their probes with a source voltage and the pad 1 is supplied with the input signal IN. The pad 5 is coupled to a measuring instrument for detecting the output signal OUT which has been amplified by the amplifier circuits 2 and 4.
Such a probing test however has a limitation that the band of frequencies to be measured is rather low. More particularly, signals of a given frequency or lower (for example, 1 MHz) only can be measured by the system. In a semiconductor device designed for amplification of high-frequency signals of, e.g., 100 MHz, the frequency of less than 1 MHz causes the coupling capacitor 3 to increase in impedance, thus interrupting normal transmission of an output of the amplifier circuit 2 to the amplifier circuit 4.
For compensation, the pad 8 is connected to the output of the amplifier circuit 2 for monitoring the output of the amplifier circuit 2. Also, an extra input signal is introduced from the pad 9 to the amplifier circuit 4 for monitoring the output signal OUT released at the pad 5. In a traditional manner, the two amplifier circuits 2 and 4 are measured separately for inspecting the semiconductor device.
As the two amplifier circuit 2 and 4 joined by the coupling capacitor 3 have to be measured separately in the conventional semiconductor device, the inspection will be troublesome and time consumable.
Also, the separate inspection for the two amplifier circuits 2 and 4 requires the two test pads 8 and 9 for their respective amplifier circuits 2 and 4, hence increasing the overall size of the semiconductor IC device.